Final answer:
Cells are the basic units of structure and function in living things, while tissues, organs, and organ systems are various levels of organization in the body.
Step-by-step explanation:
The basic unit of structure and function of all living things is a cell. A tissue is a group of cells of the same kind. An organ is a structure composed of one or more types of tissues that work together to perform a specific function. Lastly, an organ system is a group of organs that work together to perform major functions or meet physiological needs of the body.